I have posted a question about this in the past but didn't find the answer, but after gassing up my ski boat and spilling gas (again) I have to ask (again).

Every boat I have ever owned, from 16-18 ski boats, 25' center console, 36' sport fish, and several different sailboats, while fueling up when the tanks reach full the fuel squirts out of the fill pipe and/or the vent.

This happens with more or less fuel spurting out every single time, no matter what I do unless I stop filling with the tank partly filled. I try filling faster and slower, stop occasionally to make sure the vents aren't building back pressure in the tank. Nothing works.

BUT!!! I have never owned a car or truck that did this. Pull up to a pump and blow fuel in as fast as possible and the cutoff clicks and nary a drop on the ground.

The reason cannot be from the nozzle or fill system because I have many times pulled up to a station with boat on trailer and truck, filled both from the same nozzle. Boat spills, truck doesn't.

So why????? What is the difference between boat fill systems and car fill systems? Is there a different or larger vent line to car tanks? How can I rig my boat so I don't spill fuel? Am I the only one this happens to? Is there some secret that no one every shared with me?

So far the only partial solution I have is wrap a rag around the nozzle to block the mouth of the fill. Then the fuel just soaks the rag and sometimes a small amount spurts out the vent.

I really want to figure this out. I hate spilling diesel on my deck and worse, into the water. I have tried the little whistle thingy in the vent line and some other gadget and neither did a thing. I'm guessing it has something to do with the venting system but what?

__________________

__________________
The water is always bluer on the other side of the ocean.

I use the fuel gauge on the boat and stop when it shows full, because otherwise exactly the same happens.

From your reply I guess you have the same problem?

I have done what you suggest to some extent but doesn't always work well. For example, on my ski boat I have to turn on the ignition and get someone to sit in the boat to watch the gauge but even then it is very inaccurate, not calibrated and doesn't go up/down in a linear way with the amount of fuel in the tank.

On my current sailboat their is no external gauge so I have to get someone below looking at the little dial gauge on top of the tank which is also not 100% accurate and also awkward. Plus when it shows full there is still room for several gallons which can be very good to have on a long trip.

Really want to know how to fill until the handle clicks off without dumping fuel. There must be a way.

__________________
The water is always bluer on the other side of the ocean.

You may be filling too quickly. Boat vents and car vents are completely different. You can do some homework on how car fuel tanks are vented and how the nozzles work.

We use the engine hours as our fuel gauge and have determined our average fuel use of approx. 0.5 gph and fill that way: 20 hours = 10 gallons.

Yoou also have to change your mindset: it does NOT have to be completely topped off as you would with a car.

Your boat, your choices.

Thanks Stu,

This just came up in \ my previous reply, sometimes I really like to completely fill the tank. Long cruises, long way from refueling stops, etc. Topping off an extra 5 gallons can mean an extra 40-50 miles cruising range. Since I have dual tanks that could be 100 miles. On a long passage that's very significant.

I have tried filling very slowly and still have fuel blow back. Maybe not quite as much but still happens.

So you're saying it's due to the vent, which is what I suspect. Couldn't a boat tank vent be set up the same way as a car tank vent?

__________________
The water is always bluer on the other side of the ocean.

5 gallons is a BIG difference, and i simply do NOT have this problem on a 23 gallon tank.

No, the vents on a boat are different than a car, which is why I suggested you do some "homework." Using the nozzle to click off on a boat is simply asking for an overflow through the vent, which in most cases HAS TO BE below the fuel point. Waiting for the nozzle to click will ensure a leak through the vent.

If you want to absolutely insure that you have a full tank, go very slowly and wrap a rag around the vent, NOT the fuel fill hole.

Modern cars have fuel tanks that don't vent to the atmosphere, they have a canister that absorbs the fuel vapors and it gets released into the engine by electronic controls. The tank vent is a one-way check valve that only allows air in, not out. It is complicated, an in fact very important for pollution. A boat has just a simple vent that overflows when the tank is full (maybe big ones are different). You could rig a more accurate gauge for detecting full and put a led display near the fill would be an idea.

Car fills are rarely over 2 feet and often much less as well as running very vertical. It' a wide open dump into the tank. I believe the vent goes right back into the fill tube at the top on most.
Boats have vent tubes that may be very long and often have low or horizontal areas. Ditto for the fill tubes. If you want to rid yourself of the issue entirely fill the tank directly on top of the tank would be one way. I have seen metal boats with a fill "compartment"... simply a box that the fill opening and the vent are in. No surge from the vent or fill exits the box. Also have seen many boats with the fill on the cockpit floor going maybe a foot down to the tank.... easy and fast to fill.

__________________"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard

Cheechako has the answer, I think. We have used rags, diesel soaker pads, sight gauges, electric gauges, those pump up thingymajiggies that willl tell you how full each of 6 different tanks (tank tenders) are along with the whistle attachment and sounding tanks with a wooden stick through an access hole in the top of the tank. The last method finally revealed how to fill a tank almost full without the spillage. We would drag the diesel hose down to the top of the tank and fill through the access hole. We only had 3 tanks, 1X800 gal and 2X500 gal so it wasn't any big drama to fill them 95% full. No spillage using that method. On another vessel that I still drive occasionally, she has 6 tanks ranging from 500 to 800 gallons with no access through the top of the tank other than the filler hose and vent. Slow feed rate is the only way to ensure spillage is minimized. If you have ever filled a plastic 5 gallon tank at a gas pump, you can see how easy it is to get it completely full to the filler hole because you're venting at the same rate you are filling and you can see the fuel rising to the top of the tank. My guess is that if you had a vent hole the size of your filler hole, short run from nozzle to tank and good sight on rising fuel level, your problem would be solved. Phil

So its not just me that suffers from this problem. In my case, its just the vent the spits out the odd drops of diesel.
I figure in my case that its due the relatively large diameter of the filling hose (3") compared to the vent hose (.75") and the little skin fitting for the vent on the boats side reducing that even further.
On top of that, I reckon that when sailing, with the boat heeled, fuel gets sloshed into the vent line, and not all of it drains back.
Solution so far is to fill slowly,and have someone hold an oil absorbent pad under the vent to catch the drops.
There used to be a little gizmo on the market, it was a small container with an opening designed to go over the vent fitting at the boats side, and a couple of suction cups to hold it place, the theory being this would catch the drops, but it is no longer made, so maybe it was not as successful as was hoped.

On a ships bunker tanks, the vent area is much larger than the filling pipe. On my tug, the filling lines into each tank is 6", and each tank is served with two 6" vents, and there is never any problem when bunkering.

Ideally on a boat would be a deck mounted gooseneck vent which you could place a jar under when filling, but the disadvantage is that the gooseneck would be susceptible to damage.

5 gallons is a BIG difference, and i simply do NOT have this problem on a 23 gallon tank.

No, the vents on a boat are different than a car, which is why I suggested you do some "homework." Using the nozzle to click off on a boat is simply asking for an overflow through the vent, which in most cases HAS TO BE below the fuel point. Waiting for the nozzle to click will ensure a leak through the vent.

If you want to absolutely insure that you have a full tank, go very slowly and wrap a rag around the vent, NOT the fuel fill hole.

Hi Stu,

Unlike some posters on internetforums I did do a bit of homework on car vent systems.

SI have googled various search terms but so far I only came up with part numbers, carbon filter diagrams, some parts blowups and some details about where/how to clear a clogged vent on older cars but nothing that gave me a description of the theory, practice and how they generally work and how I might design or build one.

In my current boat the fill is flush on the deck and the vent on the cabin trunk so the vent is 12-18" higher than the fill and I don't get any fuel out of the vents, just out of the fill. They are 2 X 40 gallon tanks, very long and skinny (fit under the settees), odd shaped and much larger at the fill end which is why the big potential capacity loss. Losing a couple of inches at the top of a 6' long tank adds up.

Believe me, I do the slow fill and rag technique (sometimes to the annoyance of the attendant at the fuel dock but oh well) and that does reduce the blowback a lot but still get it and catch most but sometimes not all of it in the rag.

I know I can avoid spills by various techniques but it sure would be nice and simplify fueling if I could mindlessly fill the boat the same way I fill the car. Not to mention that it is annoying to kneel on the deck in the hot sun for 5-10 minutes waiting expectantly for diesel fuel to coat my hands and end up with a fuel soaked rag to deal with.

If you could point me to a link or something that describes an automotive system and give me some kind of idea as to how I might do the same on a boat it would be appreciated.

__________________
The water is always bluer on the other side of the ocean.

I used to regularly spill a small amount of gasoline when fueling my Grady White until I bought a "No Spill" fuel recovery device. It's a small bottle with a hole in the side and suction cups, which you place over the vent so that the dribbles go directly into the bottle. Never had a problem after I bought one. Found it at West Marine.

If you already keep a log of your fuel hours, so you can determine approximately how much fuel per tank you will need, then you could fill about 90% full, and only go super slow the last 10%. Use the rag or the fuel saver device, as well. Allow plenty of time, so you aren't rushed when you need to go slowly.

Car fills are rarely over 2 feet and often much less as well as running very vertical. It' a wide open dump into the tank. I believe the vent goes right back into the fill tube at the top on most.
Boats have vent tubes that may be very long and often have low or horizontal areas. Ditto for the fill tubes. If you want to rid yourself of the issue entirely fill the tank directly on top of the tank would be one way. I have seen metal boats with a fill "compartment"... simply a box that the fill opening and the vent are in. No surge from the vent or fill exits the box. Also have seen many boats with the fill on the cockpit floor going maybe a foot down to the tank.... easy and fast to fill.

I had thought about the impact of the longer fill hose in boats, but in the case of my ski boat the fill hose length is pretty similar to the tow vehicle. It does curve around a bulkhead a bit so isn't a straight drop into the tank so maybe that's an issue.

Don't think I want to fill directly into the top of the tanks in my sailboat since they're in the main cabin. One little screwup and I'm smelling diesel for the next year.

The fill box is an interesting idea but would take a lot of work in my case. Too many other things on the list.

Thanks
Skip

__________________
The water is always bluer on the other side of the ocean.

Cheechako has the answer, I think. We have used rags, diesel soaker pads, sight gauges, electric gauges, those pump up thingymajiggies that willl tell you how full each of 6 different tanks (tank tenders) are along with the whistle attachment and sounding tanks with a wooden stick through an access hole in the top of the tank. The last method finally revealed how to fill a tank almost full without the spillage. We would drag the diesel hose down to the top of the tank and fill through the access hole. We only had 3 tanks, 1X800 gal and 2X500 gal so it wasn't any big drama to fill them 95% full. No spillage using that method. On another vessel that I still drive occasionally, she has 6 tanks ranging from 500 to 800 gallons with no access through the top of the tank other than the filler hose and vent. Slow feed rate is the only way to ensure spillage is minimized. If you have ever filled a plastic 5 gallon tank at a gas pump, you can see how easy it is to get it completely full to the filler hole because you're venting at the same rate you are filling and you can see the fuel rising to the top of the tank. My guess is that if you had a vent hole the size of your filler hole, short run from nozzle to tank and good sight on rising fuel level, your problem would be solved. Phil

Sounds like you have had to deal with this to a much greater degree than I have. I have wondered if a larger vent line would make any difference but if I recall, the vent lines I have seen on a car tank weren't particularly large.

__________________

__________________
The water is always bluer on the other side of the ocean.